pm_arena.c

#include "prism/util/pm_arena.h"
 
#include <assert.h>
 
#define PM_ARENA_BLOCK_SIZE(data_size) (offsetof(pm_arena_block_t, data) + (data_size))
 
#define PM_ARENA_INITIAL_SIZE 8192
 
#define PM_ARENA_GROWTH_INTERVAL 8
 
#define PM_ARENA_MAX_SIZE (1024 * 1024)
 
static size_t
pm_arena_next_block_size(const pm_arena_t *arena, size_t min_size) {
    size_t size = PM_ARENA_INITIAL_SIZE;
 
    for (size_t exp = PM_ARENA_GROWTH_INTERVAL; exp <= arena->block_count; exp += PM_ARENA_GROWTH_INTERVAL) {
        if (size < PM_ARENA_MAX_SIZE) size *= 2;
    }
 
    return size > min_size ? size : min_size;
}
 
static pm_arena_block_t *
pm_arena_block_new(pm_arena_t *arena, size_t data_size, size_t initial_used) {
    assert(initial_used <= data_size);
    pm_arena_block_t *block = (pm_arena_block_t *) xmalloc(PM_ARENA_BLOCK_SIZE(data_size));
 
    if (block == NULL) {
        fprintf(stderr, "prism: out of memory; aborting\n");
        abort();
    }
 
    block->capacity = data_size;
    block->used = initial_used;
    block->prev = arena->current;
    arena->current = block;
    arena->block_count++;
 
    return block;
}
 
void
pm_arena_reserve(pm_arena_t *arena, size_t capacity) {
    if (capacity <= PM_ARENA_INITIAL_SIZE) return;
    if (arena->current != NULL && (arena->current->capacity - arena->current->used) >= capacity) return;
    pm_arena_block_new(arena, capacity, 0);
}
 
void *
pm_arena_alloc_slow(pm_arena_t *arena, size_t size) {
    size_t block_data_size = pm_arena_next_block_size(arena, size);
    pm_arena_block_t *block = pm_arena_block_new(arena, block_data_size, size);
    return block->data;
}
 
void
pm_arena_free(pm_arena_t *arena) {
    pm_arena_block_t *block = arena->current;
 
    while (block != NULL) {
        pm_arena_block_t *prev = block->prev;
        xfree_sized(block, PM_ARENA_BLOCK_SIZE(block->capacity));
        block = prev;
    }
 
    *arena = (pm_arena_t) { 0 };
}